Congratulations! I couldn't have walked away from it either. Looks at first blush to be a Model 47. Is there such a number stamped on the face of the receiver behind the fore arm?
Sorry, can't help with any cartridges. I sold the .22-15's I had a couple years ago. Cartridges are impossible to find anymore. I would keep an eye out for an individual case or two and plan on breech seating with them. The cartridge was a tough sell even when it was new - black powder fouling generated by the relatively large volume case in the tiny bore was appalling. Maybe post an appeal on the ASSRA forum?
Perhaps have a couple cases custom lathe turned?
